The earth's natural resources are becoming more and more scarce as industrialization and commercialization increase throughout the world. Thus, the problem of maintaining the remaining natural resources, such as water and soil, in an uncontaminated state has been given a great amount of attention in recent years. In particular, there is a great need to address the problem of preventing ground water from coming into contact with contaminated soil and thereafter maintaining such ground water in a natural state. Additionally, problems involving the remediation of a vadose zone (a volume of soil above a localized water table and its capillary fringe within the earth), which includes volatile contaminants has been the subject of a tremendous amount of effort by engineers and scientists employed by both the government and soil remediation companies.
The great effort expended by such engineers and scientists has resulted in various methods for removing contaminants from the vadose zone. However, there has been no known method proposed for physically separating the water table from a subterraneal volume of contaminated soil and for thereafter maintaining the water table apart from the contaminated soil site without continuous pumping of groundwater which is inefficient and undesirable.
With regard to basic soil remediation methods, one such method includes soil vacuuming extraction techniques, which are now well known in the art. Examples of such techniques are described more fully in U.S. Pat. No. 4,183,407.
Another method for removing contaminants from the vadose zone includes simple excavation. This entails removal of all of the contaminated soil from the vadose zone. When this method is used, the soil may be taken to an off-site or on-site location for various processing where the contaminants are removed therefrom. The cleansed soil can then be placed back into the original excavation site. Alternatively, the excavated site can be filled with fresh soil while the contaminated soil is appropriately disposed elsewhere.
Still other techniques include steps for removing contaminants from soil located beneath the water table itself. These techniques teach the injection of air into the contaminated soil beneath the water table to urge contaminants therefrom into the vadose zone above the water table and ultimately into a withdrawal well similar to the wells used for soil vacuuming extraction techniques. This method for removing contaminants is described more fully in U.S. Pat. Nos. 4,809,673 and 4,183,407.
None of the foregoing techniques address methods for lowering the water table beneath the contaminated earth to expose a vadose zone including contaminants so that the water table can be maintained remote from such contaminants. In this regard, the prior art has not presented any method for isolating a contaminated vadose zone apart from the water table after the water table has been lowered. Additionally, the prior art has not posed a solution for maintaining the water table at a predetermined lower depth after it has been lowered.
Still further, the only solution posed in the prior art to lower the water table has been to pump water therefrom until the water table has been lowered and the vadose zone has been exposed. This method presents a problem because it may be extremely expensive or even unfeasible when large amounts of ground water or when certain types of soils are present. More particularly, each type of soil has a specific hydraulic conductivity. The hydraulic conductivity is a factor which varies depending on the internal resistance of various soils, for instance the hydraulic conductivity of "loose" soil such as sand and gravel is high. Conversely, the hydraulic conductivity of "tight" soil such as silt and clay is low. Groundwater pumping is particularly difficult in soils that have low hydraulic conductivities, and under certain circumstances may be impractical or even impossible.
It should be understood that the term "soil" as used in this application is to be broadly construed, and thus, includes all types of subterraneal materials such as clay, sand, silts, standard earthen soil suitable for plant life, gravel, large stone, etc.
The present invention solves all of the aforementioned problems by disclosing new and unobvious methods for lowering the water table and maintaining same at a predetermined appropriate lower depth so that contaminants in the soil will be permanently separated from the water table. In certain instances, the water table may become improved through a natural attenuation process. The present invention also provides a new and unobvious method for lowering the water table, isolating the vadose zone by forming a hydraulic seal, and thereafter remediating the altered vadose zone. Finally, the present invention provides a new method for simply maintaining a water table at a lower depth, regardless of how the water table is lowered to such depth, and thereafter either permanently isolating the water table from volatile contaminants located in the vadose zone or remediating same.